Not Applicable
1. Field of the Invention
The present invention relates generally to the testing of the sealing capability of isolation valves in commercial and industrial fluid transport systems, and more particularly to an apparatus and method for simply and economically detecting leaky valves while the transport system remains on-line.
2. Background of the Invention
In many commercial and industrial fluid transport systems, isolation valves are employed as a defense against the incremental development of hazardous operating conditions. As a result of their simple design, these valves are generally maintained in either an open or closed position for the majority of their operational lives; the particular operational position depends primarily upon the process environment in which the valve is employed. Such isolation valves, unlike more sophisticated modulating control valves, which can be monitored and diagnosed for fluid leakage by periodic comparison of the valve position and the flow rate within the fluid path in which the valve is disposed, can generally be monitored and diagnosed while the fluid transport system remains on-line by either of the following previously known methods:
First, high frequency acoustical systems can be used to identify leaky valves under certain process conditions. For example, on-line detection of leaks can be effected using high frequency acoustics when a monitored isolation valve is set in a closed position and a significant pressure gradient exists within the valve along the directional axis of the flow path. One or more pressure sensors can then be used to xe2x80x9clistenxe2x80x9d for high frequency noise created by valve leakage.
One drawback to such a configuration is that, since the valve must first be completely closed in order to monitor or diagnosis fluid leakage, process performance of the entire system is effectively impeded for the duration of each of the respective functions. Moreover, since a significant pressure gradient must exist across the valve in order for a leak to be detected by the sensors, minor leaks may go undetected during a given testing cycle, and only later become apparent, perhaps after a significant escalation of hazardous process conditions has already occurred, or even after the valve has failed entirely. Finally, since valves in which only one of several seals has failed will not generally exhibit a significant pressure gradient along the flow path, partially leaky valves can also go undetected for some time.
As seen in U.S. Pat. No. 6,128,946 to Leon et al., on-line detection of leaks may also be accomplished using a system in which a series of pulsations within the transport system (caused by fluid vibrations) are compared to pulsations occurring within a valve""s inner cavity as a function of time. Such a configuration requires disposition of at least two pressure sensors, one located within the system""s flow path at a predetermined position either upstream or downstream relative to the valve, and another within the valve""s inner cavity. The pulsations measured by the sensors can then be used to determine whether the sensed pressure pulsations within the transport system are being passed through at least one of the seals into the valve""s inner cavity, thereby revealing the presence of leaky seals within the valve.
However, since the system taught by Leon et al. also requires, at minimum, a plurality of transducers, an analyzer to perform pulsation comparisons, and an appropriate transport system process connection disposed within a relatively close proximity of the valve to function effectively, those of ordinary skill in the art have found the configuration to be unnecessarily cumbersome and expensive, and of limited application in transport systems having an unusually complex geometry.
Finally, leaky valves may also be detected by applying an external pressure source directly to the isolation valve""s inner cavity; an operator or other maintenance personnel can then directly measure the leak rate into the valve and assess the integrity of the seals. Those of skill in the art have also found this approach dissatisfactory, however, since the fluid transport system must first be taken off-line to perform either testing or maintenance (because internal process pressures on the valve must be interrupted to determine whether the seals are leaking back into the flow path), and both an external source of pressure and additional operational personnel are required.
Accordingly, it is apparent there is a widespread need for a method and apparatus for simply and economically detecting leaky valves while a fluid transport system remains continuously on-line.
3. Objects of the Invention
In view of the foregoing, an object of the present invention is to provide an apparatus for detecting leaky valves in a commercial or industrial fluid transport system, the apparatus comprising a valve body having at least an inner cavity isolated by a plurality of seals; a vent port; a pressure sensor; a vent valve; and an exit vent, wherein the inner cavity can be pressurized and vented to an external environment under full on-line process pressure.
A further object of the invention is to provide a method for simply and economically testing the integrity of a valve seal in an on-line fluid transport system, wherein the method comprises first venting the contents of a isolation valve""s inner cavity to an external environment, and then comparing the vented inner cavity pressure to the ambient pressure of the external environment to determine whether the valve""s seals have been compromised.
An apparatus for on-line testing of isolation valves in fluid transport systems is provided comprising an upstream pipe; a downstream pipe; and a isolation valve connected therebetween for isolating fluid flow through the transport system; wherein the isolation valve has at least one upstream seal, one downstream seal, and an inner cavity effectively isolated from the fluid flow by the seals. The apparatus further comprises a pressure sensor and a vent valve, wherein the vent valve is in fluid communication with the apparatus"" inner cavity to permit venting of the fluid to an external environment when the vent valve is opened, and the pressure sensor measures a resulting difference in fluid pressure within the cavity when the vent valve is closed, said pressure difference being indicative of the integrity of the upstream and downstream seals.
The present invention also provides a method of employing the claimed apparatus in commercial and industrial fluid transport systems wherein the inner cavity can be vented under full on-line process pressure in a manner such that an observer (or a data processor) can determine whether the integrity of the valve seals has been compromised.